1. Field of the Invention
This invention relates to a radiation detecting system suitable for applying to a radiation image taking system such as an X-ray system.
2. Description of the Related Art
There has been known a radiation image taking system in which a radiation detecting system (including a semiconductor as a main part) which detects radiation and converts it to an electric signal in the medical field radiation image taking for diagnosis. As the radiation detecting system, there have been known a direct conversion system where radiation is directly converted to an electric charge, and the electric charge is stored, and an indirect conversion system where radiation is once converted to light by a scintillator such as of CsI:Tl or GOS(Gd2O2S:Tb), and the light is converted to an electric charge by a photoconductive layer and the electric charge is stored. Further, from the read-out system, the radiation detecting system can be broadly divided into a so-called optical read-out system where, the radiation is read out by the radiation detector by the use of semiconductor material which generates electric charges upon exposure to light and to a system (will be referred to as “the TFT system”, hereinbelow), where the electric charges generated in response to projection of radiation are stored and the stored electric charges are read out by turning on and off an electrical switch such as a TFT transistor (thin film transistor) by one pixel by one pixel.
In the radiation detecting system of the direct conversion system, radiation is detected by applying a predetermined bias voltage to a voltage applying electrode formed on the surface of a radiation-sensitive semiconductor layer (recording photoconductive layer), and collecting the carriers generated in response to projection of radiation with a carrier collective electrode formed on the back surface of the semiconductor layer to take out as the radiation detecting signal, and the recording photoconductive layer is often formed of an amorphous-Se (a-Se) because of advantage that it exhibits a high dark resistance, and is excellent in response.
However, when the recording photoconductive layer is formed and then a first electrode layer is formed on the surface thereof, the Se layer in the amorphous state gives rise to a problem that crystallization is promoted in an interface thereof due to heat during deposition in formation of the first electrode layer or contact with the electrode material. Since the crystallization in an interface increases the current injection from the first electrode upon recording the radiation image information, this makes noise and deteriorates the S/N. When a transparent oxide layer is used as the electrode material, especially when an ITO or IZO is used as the electrode material, the crystallization is remarkably promoted in an interface between the electrode material and the a-Se.
There has been provided a suppressing layer for suppressing an interface crystallization of a recording photoconductive layer of an organic polymer between a first electrode from which the recording light is irradiated, and the recording photoconductive layer to which the recording light is irradiated in order to avoid a problem an interface crystallization of a recording photoconductive layer. However, when a suppressing layer of an organic polymer is used, for instance, in the case where that a radiation image is recorded by a large amount of radiation and that the image is read out are repeatedly conducted, the electric charges remain in the suppressing layer, which gives rise to a problem of deterioration in sensitivity or remaining of a ghost image. Accordingly, it has been proposed to form the suppressing layer which is formed between the first electrode and the recording photoconductive layer to suppress the interface crystallization of a recording photoconductive layer by an organic film (insulating organic polymer) which exhibits insulation to electric charges opposite in polarity to the electric charges moving to the first electrode upon recording image information and exhibits conductivity to electric charges the same in polarity as the electric charges moving to the first electrode upon recording image information. (U.S. Pat. No. 7,002,173).
On the other hand, there is disclosed in Japanese Unexamined Patent Publication No. 2006-156555 that in a two-dimensional X-ray detecting system having an X-ray converting film, a first electrode formed on one side of the X-ray converting film, a second electrode formed on the other side of the X-ray converting film, and an organic film intervening between the X-ray converting film and the second electrode, the organic film may be selected from acrylic series organic resin, polyimide, PCB, PVA, acryl, polyethylene, polycarbonate, polyetherimide or conductive polymer, and it contains pigment or conductive metal or conductive carbon.
However, the insulating organic polymer involves a problem that the expected function of electron transfer cannot be sufficiently obtained. This is because it also works as an electron block layer while it is excellent in blocking the holes.